I don't see what other objects than "this" could be used here. I tried current Thread it also failed. I don't see in the previous solutions a clue (but I might have missed it) and after research on internet I only find "this" or a specific object already created like an instance with is created using a field in the class etc. But I don't find anything related on the exercice where there are no explicitly created objects of Solution. Can someone give me a hint? EDIT: the "new object" was just one of my many attempts on IntelliJ